1. Field of the Invention
The present invention relates to a manually operated trigger type dispenser which comprises a trigger, a cylinder and a piston provided in the cylinder and connected to the trigger and in which liquid is sucked into the cylinder and pressurized therein and made to flow out when the trigger is pulled to reciprocate the piston in the cylinder.
2. Description of the Prior Art
The destruction of the ozone layer is now a great environmental problem. Hence, more and more attention is drawn to manually operated trigger type dispensers which use no Freon gas and in which the piston is reciprocated in the cylinder to force out liquid. A dispenser of this type is removably connected to a container holding liquid, by means of a bottle cap set in engagement with the male screw made on the mouth of the container.
A manually operated trigger type dispenser comprises a dispenser body, a cylinder, a piston provided in the cylinder, a trigger connected to the piston, a suction tube, and a nozzle. In the dispenser, liquid is sucked upward from a container through the suction tube, forming a flowing-in passage which communicates with the suction tube. The dispenser has a flowing-out passage which connects the orifice (outlet port) of the nozzle to the cylinder. In the flowing-in passage, a first one-way valve (primary valve) is provided to control the flow of liquid from the container to the cylinder. In the flowing-out passage, a second one-way valve (secondary valve) is provided to control the flow of liquid from the cylinder to the orifice.
The trigger is swingably attached to the dispenser body which has a substantially U-shaped cross-section. Biased by a return spring, the trigger stays at its projecting position (initial position). When pulled against the urging force of the return spring, the trigger is swung to its pulled position, causing the piston to slide in the cylinder. When the trigger is released, it is swung back to the initial position due to the urging force of the return spring.
As the trigger returns from the pulled position to the initial position (i.e., the projecting position), the piston is moved, also from its pushed-in position to its initial position. As a result, the interior of the cylinder is negatively pressurized, opening the primary valve and closing the secondary valve. By virtue of the negative pressure, the liquid flows from the container into the cylinder through the suction tube, the flowing-in passage and the primary valve.
When the trigger is pulled again, the piston is moved to the pushed-in position, pressurizing the liquid in the cylinder. The liquid thus pressurized, closes the primary valve, flows into the flowing-out passage, pushes the secondary valve open, and flows outwards from the orifice (outlet port) of the nozzle.
The secondary valve tightly contacts a valve seat by virtue of the urging force of a valve spring, preventing the liquid from leaking from the cylinder. If the valve spring has a small urging force, the secondary valve is opened before the liquid in the cylinder is pressurized sufficiently and the liquid then flows out. Not sufficiently pressurized yet, the liquid flows out in drops, not in the form of a spray stream which extends for some distance as is desired. Particularly, in a manually operated trigger type dispenser which has a spinner (a member for forming an eddy flow) at the back of the orifice, it cannot make an eddy flow unless it is pressurized sufficiently. Consequently, it flows out but not in the form of a spray stream.
If the spring of the secondary valve has a great urging force, the liquid in the cylinder cannot flows out unless it is pressurized sufficiently. If the liquid is pressurized sufficiently, it can be forced out in the form of a spray stream. To pressurize the liquid sufficiently, however, the trigger needs to be pulled with a great force. This would make it difficult for physically feeble persons to use the trigger type dispenser.
All liquid pressurized in the cylinder does not flow out; a part of it remains in the cylinder. Nor does all liquid forced from the cylinder flow out from the orifice; a part of it remains in the flowing-out passages which extends from the cylinder to the orifice. When the trigger is released and the piston is thereby moved to the initial position, the interior of the cylinder is negatively pressurized. The resultant negative pressure causes the liquid remaining in the flowing-out passage to flow back into the cylinder. All liquid in the flowing-out passage does not flow back into the cylinder; a part of it still remains in the flowing-out passage.
Due to the negative pressure in the cylinder, the liquid in the container is sucked into the cylinder. The liquid drawn up into the cylinder is under normal pressure before the trigger is pulled again. By contrast, the liquid remaining in the cylinder is still pressurized and under a higher pressure. Hence, the liquid in the cylinder, i.e., the mixture of the liquid sucked from the container and the liquid remaining in the cylinder, is under a residual pressure somewhat higher than normal pressure. Due to the residual pressure, the liquid remaining in the flowing-out passage is liable to dribble from the orifice. This tendency is particularly conspicuous if the spring of the secondary valve has a small force.